Pejman Keikhaei Dehdezi

Bio: Pejman Keikhaei Dehdezi is an academic researcher from University of Nottingham. The author has contributed to research in topics: Thermal diffusivity & Aggregate (composite). The author has an hindex of 8, co-authored 13 publications receiving 275 citations. Previous affiliations of Pejman Keikhaei Dehdezi include SINTEF & URS Corporation.

Influence of the Thermophysical Properties of Pavement Materials on the Evolution of Temperature Depth Profiles in Different Climatic Regions

Abstract: The paper summarizes the relative influence of different pavement thermo-physical properties on the thermal response of pavement cross-sections, and how their relative behaviour changes in different climatic regions. A simplified one-dimensional heat flow modelling tool was developed to achieve this using a finite difference solution method for studying the dynamic temperature profile within pavement constructions. This approach allows for a wide variety and daily varying climatic conditions to be applied, where limited or historic thermo-physical material properties are available, and permits the thermal behaviour of the pavement layers to be accurately modelled and modified. The model was used with available thermal pavement materials properties and with properties determined specifically for the study reported here. The pavement materials included in the study comprised both conventional bituminous and cementicious mixes as well as unconventional mixtures that allowed a wide range of densities, thermal conductivities, specific heat capacities and thermal diffusivities to be investigated. Initially, the model was validated against in-situ pavement data collected in the USA in five widely differing climatic regions. It was found to give results at least as good as others available from more computationally expensive approaches such as 2D and 3D FE commercial packages. Then the model was used to compute the response for the same locations had the thermal properties been changed by using some of the unconventional pavement materials been used. This revealed that reduction of temperature range by several degrees was easily possible (with implications for reduction of rutting, fatigue and the Urban Heat Island effect) and that depth of penetration of peak temperatures was also achievable (with implications for winter freeze-thaw). However, the results showed that there was little opportunity to displace the peak temperatures in time.

Thermal, mechanical and microstructural analysis of concrete containing microencapsulated phase change materials

Abstract: This paper studies the thermal, mechanical and microstructural aspects of concrete containing different amounts of microencapsulated phase change materials (PCMs). In addition, numerical simulation is carried out to study the potential application of PCM-modified concrete for reduction in summer surface temperature. It is shown that increasing PCM content in concrete led to lower thermal conductivity and an increase in the heat storage ability of concrete. However, the compressive and flexural strength of concrete significantly decreased. Microstructural analysis showed that PCMs appear to remain intact during mixing; however, PCM particles appear to fail by bursting under loading, creating hemispherical voids and crack initiation points as well as possible entrapped air behaviour. The result of numerical simulation revealed that reduction in summer concrete pavement surface temperature by several degrees was possible, with implications for reduction in concrete thermal stresses, shrinkage and urban heat island effect.

Physico-mechanical, microstructural and dynamic properties of newly developed artificial fly ash based lightweight aggregate – Rubber concrete composite

Abstract: The use of industrial by-products in concrete would increase the sustainability of the construction industry. In this study, the potential use of scrap crumb rubber as fine aggregate in lightweight (Lytag) concrete was experimentally investigated. The effects of replacing natural sand by crumb rubber particles on the physico-mechanical, micro-structural and dynamic properties of the Lytag concrete were evaluated. When the rubber was introduced, the reduction in compressive strength of the Lytag concrete was experienced due to the less than perfect bond between the cement paste and the rubber as confirmed by the micro-structural observation. Additionally, there was flocculation of some of the crumb rubber particles and the packing of the rubber particles contributed to pockets of voids resulted in anisotropy in the concrete. The results also showed that the rubber not only meliorated the resistance of the cementitious Lytag composite to cracking from impact load but overall impact strength was also improved as the rubber particles acted as impedance to crack initiation and propagation.

Enhancing thermal properties of asphalt materials for heat storage and transfer applications

Abstract: This paper considers extending the role of asphalt concrete pavements to become solar heat collectors and storage systems. The majority of the construction cost is already procured for such pavements and only marginal additional costs are likely to be incurred to add the necessary thermal features. Therefore, asphalt concrete pavements that incorporate aggregates and additives such as limestone, quartzite, lightweight aggregate, copper slag, and copper fibre are designed to make them more conductive, or more insulative, or to enable them to store more heat energy. The resulting materials are assessed for both mechanical and thermal properties by laboratory tests and numerical simulations and recommendations are made in regard to the optimum formulations for the purposes considered.

Enhancement of Soil Thermo-Physical Properties Using Microencapsulated Phase Change Materials for Ground Source Heat Pump Applications

Abstract: Soil can be modified with Phase Change materials (PCM) in order to enhance its thermophysical properties and energy storage for ground source heat pump applications. This paper studies thermo-physical properties of soil modified with different amount of microencapsulated PCM. It is shown that increasing PCM amount in soil lead to lower thermal conductivity and increase of volumetric heat capacity of PCM-modified soil across the PCM melting temperature range. In addition, numerical simulation is performed to study the potential application of PCM modified soil for reduction of temperature variations in ground. The result of numerical simulation revealed that temperature variation under PCM-modified soil can be reduced by up to 3oC compared to conventional soil.

American Society for Testing and Materials

Abstract: The American Society for Testing and Materials (ASTM) is an independent organization devoted to the development of standards.

A review of energy storage types, applications and recent developments

Abstract: Energy storage technologies, including storage types, categorizations and comparisons, are critically reviewed. Most energy storage technologies are considered, including electrochemical and battery energy storage, thermal energy storage, thermochemical energy storage, flywheel energy storage, compressed air energy storage, pumped energy storage, magnetic energy storage, chemical and hydrogen energy storage. Recent research on new energy storage types as well as important advances and developments in energy storage, are also included throughout.

A review on hydronic asphalt pavement for energy harvesting and snow melting

Abstract: Solar energy is undoubtedly the environment friendly and inexhaustible energy resource for humans. The concept of hydronic asphalt pavement (HAP) is an emerging renewable energy technology, which provides an interesting method for solar energy utilization. The innovation of HAP is to mitigate a series of realistic problems related to the asphalt pavement as well as the depletion of fossil energy resource. Fluid circulating through the pipes network imbedded in the asphalt pavement can capture the solar energy and store for later use. This paper summaries the major achievements of the existing literatures about the HAP and gives some proposals for further investigations. Studies have confirmed the feasibility of harvesting solar energy, cooling the pavement, snow melting/deicing as well as air conditioning of buildings by applying innovation technologies on asphalt pavement. As seasonal energy storage technology is relatively mature at present, most of the literatures reviews focus on the influences of variables associated with system behavior as well as the heat transfer processes during snow melting and solar energy collection. Future work should aim to do more urgent issues involved with HAP application: construction technology, maintenance technology, and long-term performance. Solving these problems can strengthen the theoretical and practical understanding of HAP, and lead to more extensive applications.

Microencapsulated phase change materials for enhancing the thermal performance of Portland cement concrete and geopolymer concrete for passive building applications

Abstract: Concretes with a high thermal energy storage capacity were fabricated by mixing microencapsulated phase change materials (MPCM) into Portland cement concrete (PCC) and geopolymer concrete (GPC). The effect of MPCM on thermal performance and compressive strength of PCC and GPC were investigated. It was found that the replacement of sand by MPCM resulted in lower thermal conductivity and higher thermal energy storage, while the specific heat capacity of concrete remained practically stable when the phase change material (PCM) was in the liquid or solid phase. Furthermore, the thermal conductivity of GPC as function of MPCM concentration was reduced at a higher rate than that of PCC. The power consumption needed to stabilize a simulated indoor temperature of 23 °C was reduced after the addition of MPCM. GPC exhibited better energy saving properties than PCC at the same conditions. A significant loss in compressive strength was observed due to the addition of MPCM to concrete. However, the compressive strength still satisfies the mechanical European regulation (EN 206-1, compressive strength class C20/25) for concrete applications. Finally, MPCM-concrete provided a good thermal stability after subjecting the samples to 100 thermal cycles at high heating/cooling rates.

Asphalt solar collectors: A literature review

Abstract: Asphalt pavements subject to solar radiation can reach high temperatures causing not only environmental problems such as the heat island effect on cities but also structural damage due to rutting or hardening as a result of thermal cycles. Asphalt solar collectors are doubly effective active systems: as they solve the previously mentioned problems and, moreover, they can harness energy to be used in different applications. The main findings of the existing research on asphalt solar collectors are gathered together in this review paper. Firstly, the main heat transfer mechanisms involved in the solar energy collection process are identified and the most important parameters and variables are presented. After analyzing the theoretical foundations of the heat transfer process, this review focuses on the types of studies carried out so far on asphalt’s thermal behavior, different methodologies employed by other authors to study asphalt solar collectors and influence of the variables involved in thermal energy harvesting.